@papukaija I generally agree, though it is possible that the information on the Ubuntu wiki could be outdated or even wrong (since it can be edited by any registered user).
–
belacquaFeb 14 '11 at 6:11

2 Answers
2

The first five fields shall be integer patterns that specify the
following:
1. Minute [0,59]
2. Hour [0,23]
3. Day of the month [1,31]
4. Month of the year [1,12]
5. Day of the week ([0,6] with 0=Sunday)
Each of these patterns can be either an asterisk (meaning all valid
values), an element, or a list of elements separated by commas. An ele‐
ment shall be either a number or two numbers separated by a hyphen
(meaning an inclusive range). The specification of days can be made by
two fields (day of the month and day of the week). If month, day of
month, and day of week are all asterisks, every day shall be matched.
If either the month or day of month is specified as an element or list,
but the day of week is an asterisk, the month and day of month fields
shall specify the days that match. If both month and day of month are
specified as an asterisk, but day of week is an element or list, then
only the specified days of the week match. Finally, if either the month
or day of month is specified as an element or list, and the day of week
is also specified as an element or list, then any day matching either
the month and day of month, or the day of week, shall be matched.

The article you linked to looks like a good one. It's giving you some good examples and it's actually easier to read than the man-page excerpt I provided here.
You should be able to use the syntax it talks about.

will output the crontab environment's environment variables for you to work with, in your crontab. You can use maybe variables like ${HOME}, ${SHELL} to make the script cleaner and maybe use the script on another machine.